#define _CRT_SECURE_NO_WARNINGS 1
#include <stdio.h>
int main()
{
	int arr[] = { 1,2,3,4,5,1,2,3,4 };
	int sum = 0;
	int sz = sizeof arr / sizeof arr[0];
	for (int i = 0; i < sz; i++)
	{
		sum ^= arr[i];
	}
	printf("%d", sum);
	return 0;
}